Good morning AW2647.
We also have a 2004 Vectra 40 AD with the Cummins 400 ISL engine.
When we start the engine, she immediately reaches for 600 Kpa (approx 87 psi), at idle, she is normally close to 310 kpa (45 psi); and she runs under load at about 450 kpa (65 psi). I once had a Cummins shop shut her down right after start because of "high" oil pressure until I told him that this was "normal" for my engine during my time with her. He felt better after she warmed up and started to decrease. Hope this helps
Daniel & Gloria
2004 Winnebago Vectra 40AD
Blue Ox & Wrangler